• 한국전자파학회논문지
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• 제19권8호
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• pp.826-831
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• 2008

본 논문은 이동 위성 통신을 위한 성형 반사판 기반의 하이브리드 안테나 설계에 대하여 서술한다. 하이브리드 안테나는 성형 반사판과 $1{\times}8$ 배열의 선형 위상 배열 안테나로 이루어진 급전부로 구성되며, 최소의 개구면으로 안테나에 요구되는 최적의 성능을 구현하기 위하여, 반사판 성형화 기법이 적용되었다. 또한, 급전부 설계에 있어서, 능동 배열의 수를 최적화함으로써 전체적인 안테나의 제작 단가를 최소화 할 수 있다는 장점을 갖는다. Ka-대역에서 설계된 본 안테나는 앙각 방향 $+45^{\circ}$를 기준으로 ${\pm}3^{\circ}$ 범위에서 빔 패턴을 전기적으로 제어할 수 있으며, 부엽 레벨을 포함한 안테나 빔 패턴에 대해서는 ITU-R S.465-5에 만족하도록 설계되었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.44-51
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• 2019

Designing sophisticate ship structures that satisfy several design criteria simultaneously with minimum weight and cost is an important engineering issue. For a ship structure composed of a shell and stiffeners, this issue is more serious because their mutual effect has to be addressed. In this study, a two-stage optimization method is proposed for the conceptual design of stiffeners in a ship's prow. In the first stage, a topology optimization method is used to determine a potential stiffener distribution based on the optimal results, whereupon stiffeners are constructed according to stiffener generative theory and the material distribution. In the second stage, size optimization is conducted to optimize the plate and stiffener sections simultaneously based on a parametric model. A final analysis model of the ship-prow structure is presented to assess the validity of this method. The analysis results show that the two-stage optimization method is effective for stiffener conceptual design, which provides a reference for designing actual stiffeners for ship hulls.

• 한국초전도ㆍ저온공학회논문지
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• 제24권3호
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• pp.24-29
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• 2022

One of the recent proposals with nuclear magnetic resonance (NMR) is a multi-bore NMR which consists of array of magnets which could present possibilities to quickly cope with pandemic virus by multiple inspection of virus samples. Low temperature superconductor (LTS) can be a candidate for mass production of the magnet due to its low price in fabrication as well as operation by applying the helium zero boil-off technology. However, training feature of LTS magnet still hinders the low cost operation due to multiple boil-offs during premature quenches. Thus in this paper, LTS magnet with low mechanical stress is designed targeting the "training-free" LTS magnet for mass production of magnet array for multi-bore NMR. A thorough process of an LTS magnet design is conducted, including the analyses as the followings: electromagnetics, mechanical stress, cryogenics, stability, and protection. The magnet specification was set to 4.7 T in a winding bore of 85 mm, corresponding to the MR frequency of 200 MHz. The stress level is tolerable with respect to the wire yield strength and epoxy crack where mechanical disturbance is less than the minimum quench energy.

• Current Optics and Photonics
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• 제7권3호
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• pp.273-282
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• 2023

This paper presents a new method for redistributing effectively the first orders of each lens element to achromatize and athermalize an optical system, by introducing a novel method for adjusting the slope of an achromatic and athermal line. This line is specified by connecting the housing, equivalent single lens, and aberration-corrected point on a glass map composed of available plastic and glass materials for molding. Thus, if a specific lens is replaced with the material characterized by the chromatic and thermal powers of an aberration-corrected point, we obtain an achromatic and athermal system. First, we identify two materials that yield the minimum and maximum slopes of the line from a housing coordinate, which specifies the slope range of the line spanning the available materials on a glass map. Next, redistributing the optical first orders (optical powers and paraxial ray heights) of lens elements by moving the achromatic and athermal line into the available slope range of materials yields a good achromatic and athermal design. Applying this concept to design a mobile-phone camera lens, we efficiently obtain an achromatic and athermal system with cost-effective material selection, over the specified temperature and waveband ranges.

• 한국항공우주학회지
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• 제35권7호
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• pp.647-654
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• 2007

본 논문에서는 일정한 추력을 이용한 지구-달의 연료 최적 궤적해를 이용하여, 가변 추력기를 이용한 지구 탈출 궤적에서의 에너지 및 연료 최적 궤적을 설계하였다. 에너지 최적의 지구 탈출 궤적은 여러 차례 지구를 공전하게 되고, 궤도 천이 시간이 일반적인 궤도 천이 시간 보다 상대적으로 오래 소요되므로 최적화 문제를 해를 구하기가 쉽지 않다. 따라서 에너지 최적 해를 구하기 위하여, 초기 상태변수를 조정하면서 Discrete continuation의 기법을 적용하였다. 최적화 문제의 종말 조건은 일정한 추력기를 이용한 지구 탈출 궤적의 종말 조건을 이용하였고, 구속 시간은 일정한 추력기를 이용한 궤도 천이의 경우보다 큰 값으로 설정하였다. 한편, 연료 최적 궤적은 제어 입력의 형태가 불연속적이기 때문에 해를 구하기가 쉽지 않다. 따라서 연료 최적 궤적은 에너지 최적의 해와 호모토피(Homotopy) 기법을 적용시켜 그 해를 구하였다.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2444-2452
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• 2022

The field-programmable gate array (FPGA) is gaining popularity in industrial automation such as nuclear power plant instrumentation and control (I&C) systems due to the benefits of having non-existence of operating system, minimum software errors, and minimum common reason failures. Separate functions can be processed individually and in parallel on the same integrated circuit using FPGAs in comparison to the conventional microprocessor-based systems used in any plant operations. The use of FPGAs offers the potential to minimize complexity and the accompanying difficulty of securing regulatory approval, as well as provide superior protection against obsolescence. Wireless sensor networks (WSNs) are a new technology for acquiring and processing plant data wirelessly in which sensor nodes are configured for real-time signal processing, data acquisition, and monitoring. ZigBee (IEEE 802.15.4) is an open worldwide standard for minimum power, low-cost machine-to-machine (M2M), and internet of things (IoT) enabled wireless network communication. It is always a challenge to follow the specific topology when different Zigbee nodes are placed in a large network such as a plant. The research article focuses on the hardware chip design of different topological structures supported by ZigBee that can be used for monitoring and controlling the different operations of the plant and evaluates the performance in Vitex-5 FPGA hardware. The research work presents a strategy for configuring FPGA with ZigBee sensor nodes when communicating in a large area such as an industrial plant for real-time monitoring.

• 한국신뢰성학회:학술대회논문집
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• 한국신뢰성학회 2001년도 정기학술대회
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• pp.277-278
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• 2001

The successful operation of a product In service depends upon the effective provision of logistic support in order to achieve and maintain the required levels of performance and customer satisfaction. Logistic support encompasses the activities and facilities required to maintain a product (hardware and software) in service. Logistic support covers maintenance, manpower and personnel, training, spares, technical documentation and packaging handling, storage and transportation and support facilities.The cost of logistic support is often a major contributor to the Life Cycle Cost (LCC) of a product and increasingly customers are making purchase decisions based on lifecycle cost rather than initial purchase price alone. Logistic support considerations can therefore have a major impact on product sales by ensuring that the product can be easily maintained at a reasonable cost and that all the necessary facilities have been provided to fully support the product in the field so that it meets the required availability. Quantification of support costs allows the manufacturer to estimate the support cost elements and evaluate possible warranty costs. This reduces risk and allows support costs to be set at competitive rates.Integrated Logistic Support (ILS) is a management method by which all the logistic support services required by a customer can be brought together in a structured way and In harmony with a product. In essence the application of ILS:- causes logistic support considerations to be integrated into product design;- develops logistic support arrangements that are consistently related to the design and to each other;- provides the necessary logistic support at the beginning and during customer use at optimum cost.The method by which ILS achieves much of the above is through the application of Logistic Support Analysis (LSA). This is a series of support analysis tasks that are performed throughout the design process in order to ensure that the product can be supported efficiently In accordance with the requirements of the customer.The successful application of ILS will result in a number of customer and supplier benefits. These should include some or all of the following:- greater product uptime;- fewer product modifications due to supportability deficiencies and hence less supplier rework;- better adherence to production schedules in process plants through reduced maintenance, better support;- lower supplier product costs;- Bower customer support costs;- better visibility of support costs;- reduced product LCC;- a better and more saleable product;- Improved safety;- increased overall customer satisfaction;- increased product purchases;- potential for purchase or upgrade of the product sooner through customer savings on support of current product.ILS should be an integral part of the total management process with an on-going improvement activity using monitoring of achieved performance to tailor existing support and influence future design activities. For many years, ILS was predominantly applied to military procurement, primarily using standards generated by the US Government Department of Defense (DoD). The military standards refer to specialized government infrastructures and are too complex for commercial application. The methods and benefits of ILS, however, have potential for much wider application in commercial and civilian use. The concept of ILS is simple and depends on a structured procedure that assures that logistic aspects are fully considered throughout the design and development phases of a product, in close cooperation with the designers. The ability to effectively support the product is given equal weight to performance and is fully considered in relation to its cost.The application of ILS provides improvements in availability, maintenance support and longterm 3ogistic cost savings. Logistic costs are significant through the life of a system and can often amount to many times the initial purchase cost of the system.This study provides guidance on the minimum activities necessary to Implement effective ILS for a wide range of commercial suppliers. The guide supplements IEC60106-4, Guide on maintainability of equipment Part 4: Section Eight maintenance and maintenance support planning, which emphasizes the maintenance aspects of the support requirements and refers to other existing standards where appropriate. The use of Reliability and Maintainability studies is also mentioned in this study, as R&M is an important interface area to ILS.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.381-388
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• 2000

The steel piers and the concrete-filled steel piers, in spite of reasonable strength, high ductility, small section, and fast construction, have not been considered as the alternatives to the RC piers even in the highly populated urban area where aseismic safety, limited space and fast construction are indispensably required. In this paper, a steel pier and 4 box type concrete-filled steel piers were tested with the quasi-static cyclic loading to estimate the ductility and the strength. Additional devices such as base rib, turn-buckle, and anchor bolted added at the to increase the ductility with minimum additional cost. The result showed that the concrete filled-in steel piers had higher energy absorbtion and strength than steel piers had, but also showed that slight overlooking in the design and fabrication could lead to the abrupt fracture just after small local buckling at the bottom.

• ETRI Journal
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• 제40권2호
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• pp.218-226
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• 2018

Multiuser detection (MUD) and channel estimation techniques in space-division multiple-access aided orthogonal frequency-division multiplexing systems recently has received intensive interest in receiver design technologies. The maximum likelihood (ML) MUD that provides optimal performance has the cost of a dramatically increased computational complexity. The minimum mean-squared error (MMSE) MUD exhibits poor performance, although it achieves lower computational complexity. With almost the same complexity, an MMSE with successive interference cancellation (SIC) scheme achieves a better bit error rate performance than a linear MMSE multiuser detector. In this paper, hybrid ML-MMSE with SIC adaptive multiuser detection based on the joint channel estimation method is suggested for signal detection. The simulation results show that the proposed method achieves good performance close to the optimal ML performance at low SNR values and a low computational complexity at high SNR values.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 2000년도 THE THIRD INTERNATIONAL CONFERENCE ON AGRICULTURAL MACHINERY ENGINEERING. V.III
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• pp.764-769
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• 2000

A new transplant production system that produces high quality plug seedlings of specific crop has been studied. It is a plant factory designed to produce massive amount of virus free seedlings. The design concept for building this plant factory is to realize maximum energy efficiency and minimum initial investment and running cost. The basic production strategy is the sitespecific management. In this case, the management of the growth of individual plantlet is considered. This requires highly automated and information intensive production system in a closed aseptic environment the sterilized specific crops. One of the key components of this sophisticated system is the irrigation system. The conditions that this irrigation system has to satisfy are: 1. to perform the site specific crop management in irrigation and 2. to meet the no waste standard. The objective of this study is to develop an irrigation scheduling that can implement the no waste standard.